Inhibitory effect of methamphetamine on intracavernous pressure in rats

Background: There is a paucity of animal study investigating the effect of methamphetamine (METH) on penile erection in spite of its worldwide population. Aim: We investigated the changes of intracavernous pressure (ICP) elicited by cavernous nerve stimulation after a single and repeated dosing of METH in male rats. Methods: Rats were randomly assigned to five treated groups and one control group with each group having 3 rats. Rats in treated group 1, 2, and 3 received a single dose intravenous injection with 0.1, 1.0, and 10.0 μg/kg METH, respectively. Rats in treated group 4 and 5 received an intraperitoneal injection with 1.0 and 5.0 mg/kg METH four times daily for two weeks, respectively. ICP was measured during penile erection elicited by cavernous nerve stimulation. Expression of neural nitric oxide synthase (nNOS) was measured in the cavernous nerve and muscle after single and repeated dosing. Main Outcome Measures: The primary outcome measure was the ΔICP/mean arterial pressure (MAP) and the secondary was the expression of nNOS in the tissue. Results: The ΔICP/MAP increased slightly in group 1 rats and decreased substantially in group 2 and 3 rats compared with the baseline. A single dose of METH within the range of 0.1 to 10.0 μg/kg exhibited an inhibitory effect of ICP (%). The ΔICP/MAP significantly decreased in group 4 and 5 rats after repeated dosing of METH, compared with that in group 3. The expression of nNOS significantly increased in the cavernous muscle after single and repeated dosing of METH compared with the control. Conclusions: The preliminary results suggested that a single dose of METH exhibits an inhibitory effect on ICP and repeated dosing of METH exerted a greater inhibition than a single dosing. However, these results need further study